Nox sensor diagnostic system and method

ABSTRACT

A system includes: a NO x  sensor; and a controller configured to: increase an amount of O 2  in a chamber of the NO x  sensor; interpret one or more values of a parameter indicative an amount of O 2  and/or NO x  measured by the NO x  sensor; determine if the one or more values of the parameter exceed a threshold value; and indicate a failure of the NO x  sensor responsive to the one or more values of the parameter do not exceed the threshold value.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a divisional of U.S. patent application Ser.No. 14/598,906 filed Jan. 16, 2015, the contents of which areincorporated herein by reference.

TECHNICAL FIELD

The present application relates generally to the field of selectivecatalytic reduction (SCR) systems for an exhaust aftertreatment system.

BACKGROUND

For internal combustion engines, such as diesel engines, nitrogen oxide(NO_(x)) compounds may be emitted in the exhaust. To reduce NO_(x)emissions, a SCR process may be implemented to convert the NO_(x)compounds into more neutral compounds, such as diatomic nitrogen, water,or carbon dioxide, with the aid of a catalyst and a reductant. Thecatalyst may be included in a catalyst chamber of an exhaust system,such as that of a vehicle or power generation unit. A reductant such asanhydrous ammonia, aqueous ammonia, or urea is typically introduced intothe exhaust gas flow prior to the catalyst chamber. To introduce thereductant into the exhaust gas flow for the SCR process, an SCR systemmay dose or otherwise introduce the reductant through a dosing modulethat vaporizes or sprays the reductant into an exhaust pipe of theexhaust system up-stream of the catalyst chamber. The SCR system mayinclude one or more sensors to monitor conditions within the exhaustsystem.

In some instances, NO_(x) sensors may fail and output values indicativeof an amount of NO_(x) at a low level despite increases in NO_(x)concentration. In some instances, this may be especially problematic atthe exit of an exhaust system when NO_(x) concentrations are expected tobe minimal and have minimal variations.

SUMMARY

Various embodiments relate to a system including a NO_(x) sensor and acontroller. The controller is configured to interpret one or more valuesof a parameter indicative an amount of O₂ and/or NO_(x) measured by theNO_(x) sensor responsive to the NO_(x) sensor reaching an operationaltemperature and an oxygen pump of the NO_(x) sensor has not beenactivated. The controller is further configured to determine if the oneor more values of the parameter exceed a threshold value and indicate afailure of the NO_(x) sensor responsive to the one or more values of theparameter not exceeding the threshold value.

Other embodiments relate to a system including a NO_(x) sensor and acontroller. The controller is configured to increase an amount of O₂ ina chamber of the NO_(x) sensor. The controller is also configured tointerpret one or more values of a parameter indicative an amount of O₂and/or NO_(x) measured by the NO_(x) sensor. The controller is furtherconfigured to determine if the one or more values of the parameterexceed a threshold value and indicate a failure of the NO_(x) sensorresponsive to the one or more values of the parameter not exceeding thethreshold value.

Further embodiments relate to a system including a NO_(x) sensor and acontroller. The controller is configured to interpret one or more valuesof a parameter indicative an amount of O₂ and/or NO_(x) measured by theNO_(x) sensor responsive to the NO_(x) sensor reaching an operationaltemperature and an oxygen pump of the NO_(x) sensor has not beenactivated or responsive to increasing an amount of O₂ in a chamber ofthe NO_(x) sensor. The controller is also configured to calculate avariation of the one or more values of the parameter indicative of theamount of O₂ and/or NO_(x) measured by the NO_(x) sensor. The controlleris configured to determine if the calculated variation exceeds athreshold value and indicate a failure of the NO_(x) sensor responsiveto the calculated variation not exceeding the threshold value.

BRIEF DESCRIPTION OF THE DRAWINGS

The details of one or more implementations are set forth in theaccompanying drawings and the description below. Other features,aspects, and advantages of the disclosure will become apparent from thedescription, the drawings, and the claims, in which:

FIG. 1 is a block schematic diagram of an example selective catalyticreduction system having an example reductant delivery system for anexhaust system;

FIG. 2 is a block diagram of an implementation of a NO_(x) sensor havinga first chamber, a second chamber, and a reference chamber;

FIG. 3 is a block diagram of an implementation of an exemplary processfor detecting a failure of a NO_(x) sensor when the NO_(x) sensorreaches an operating temperature;

FIG. 4 is a block diagram of an implementation of another exemplaryprocess for detecting a failure of a NO_(x) sensor during operation;

FIG. 5 is a process diagram of an implementation of an exemplary processfor detecting a failure of a NO_(x) sensor when the NO_(x) sensorreaches an operating temperature or during operation using a counter fordetermining an average change in a parameter indicative of the O₂ and/orNO_(x) detected by the NO_(x) sensor over several determined values;

FIG. 6 is a graphical plot of several values for a parameter indicativeof a NO_(x) concentration level from a NO_(x) sensor, a parameterindicative of whether a dew point has been reached, a parameterindicative of whether a NO_(x) output value is stable, and a parameterindicative of an O₂ concentration level in the exhaust with a spike inthe parameter indicative of the NO_(x) concentration level from theNO_(x) sensor when the NO_(x) sensor reaches an operating temperature;

FIG. 7 is a graphical plot of several values for a parameter indicativeof a NO_(x) concentration level from a NO_(x) sensor, a parameterindicative of whether a dew point has been reached, a parameterindicative of whether a NO_(x) output value is stable, a parameterindicative of an O₂ concentration level in the exhaust, and parametersindicative of a diagnostic trigger count and a diagnostic completioncount with several spikes in the parameter indicative of the NO_(x)concentration level from the NO_(x) sensor during operation; and

FIG. 8 is a block diagram of an implementation of another exemplaryprocess for detecting a failure of a NO_(x) sensor when the NO_(x)sensor reaches an operating temperature.

It will be recognized that some or all of the figures are schematicrepresentations for purposes of illustration. The figures are providedfor the purpose of illustrating one or more implementations with theexplicit understanding that they will not be used to limit the scope orthe meaning of the claims.

DETAILED DESCRIPTION

Following below are more detailed descriptions of various conceptsrelated to, and implementations of, methods, apparatuses, and systemsfor performing a diagnostic check on a NO_(x) sensor to determinewhether the sensor has failed. The various concepts introduced above anddiscussed in greater detail below may be implemented in any of numerousways, as the described concepts are not limited to any particular mannerof implementation. Examples of specific implementations and applicationsare provided primarily for illustrative purposes.

I. Overview

In some vehicles, NO_(x) may be produced with other compounds as aresult of combustion, such as for a diesel fuel vehicle, a diesel fuelpower generator, etc. In some exhaust systems, a sensor module may belocated upstream, downstream, or as part of an SCR catalyst to detectone or more emissions in the exhaust flow after the SCR catalyst. Forexample, a NO_(x) sensor may be positioned downstream of the SCRcatalyst to detect NO_(x) within the exhaust gas exiting the exhaust ofthe vehicle. Such emission sensors may be useful to provide feedback toa controller to modify an operating parameter of the aftertreatmentsystem of the vehicle. For example, a NO_(x) sensor may be utilized todetect the amount of NO_(x) exiting the vehicle exhaust system and, ifthe NO_(x) detected is too high or too low, the controller may modify anamount of reductant delivered by a dosing module.

A NO_(x) sensor includes a portion of the NO_(x) sensor that detects theamount of NO_(x) present in the exhaust gas sample. The portion of theNO_(x) sensor that detects the amount of NO_(x) present in the exhaustgas sample may utilize a NO_(x) decomposition electrode to decomposeNO_(x) into nitrogen and oxygen ions and utilize a current generated bypumping the oxygen ions through oxygen porous material as representativeof the NO_(x) present in the exhaust gas sample. Because the portion ofthe NO_(x) sensor that detects the amount of NO_(x) present in theexhaust gas sample utilizes oxygen ions as representative of the NO_(x)present in the exhaust gas sample, the NO_(x) sensor is cross-sensitiveto any oxygen (O₂) remaining within the exhaust gas sample. Thus, theNO_(x) sensor may remove O₂ from an exhaust gas sample prior to theportion of the NO_(x) sensor that detects the amount of NO_(x) presentin the exhaust gas sample. That is, oxygen pumping electrodes presentwithin one or more chambers of the NO_(x) sensor may be used to extractand pump out O₂ present in the exhaust gas sample to reduce theremaining amount of O₂ in the exhaust gas sample to a substantiallysmall amount (e.g., 0.001 parts per million (ppm)). Thus, the currentgenerated by pumping oxygen ions through oxygen porous material issubstantially representative of the NO_(x) present in the exhaust gassample.

In some instances, such as for NO_(x) sensors at the end of an SCRsystem or tailpipe out portion of an exhaust system, the amount ofNO_(x) present in the exhaust gas sample may be a very small amount withonly minimal variation (e.g., varying by approximately ±5 ppm). Thus,the measurements from the NO_(x) sensor may be very small and vary in aminimal range during operation. However, in some instances, a NO_(x)sensor may fail when the portion of the NO_(x) sensor that detects theamount of NO_(x) present in the exhaust gas sample registers the sameminimal amount of NO_(x) despite changes to the amount of NO_(x) presentin the exhaust gas sample. For instance, the NO_(x) decompositionelectrode may fail to properly decompose NO_(x) or other failures withthe NO_(x) sensor may cause the NO_(x) sensor to be stuck in the minimalrange regardless of changes in NO_(x) concentration. Accordingly, it maybe useful to detect when the NO_(x) sensor is in this stuck-in-rangefailure mode.

Some NO_(x) sensor diagnostic implementations utilize high engine-outNO_(x) spikes to detect changes in measured NO_(x) by a NO_(x) sensor todetermine whether the NO_(x) sensor is in a stuck-in-range failure mode.However, with aftertreatment systems that reduce NO_(x) emissions tovery low levels despite these high engine-out NO_(x) spikes, such spikesmay no longer correlate with system outlet NO_(x) variation, therebyresulting in potentially diagnosing a NO_(x) sensor as in astuck-in-range failure mode when the NO_(x) sensor is actually workingproperly. Such false-positive failures may result in higher warrantycoverage costs, higher replacement part costs, etc.

Moreover, the operation of an engine may be substantially stable,thereby reducing such high engine-out NO_(x) spikes. As NO_(x) emissionsmay be needed or required to be kept at low levels over long periods oftime, the lack of high engine-out NO_(x) spikes may result in a NO_(x)sensor entering into a stuck-in-range failure mode without beingdetected for a period of time, thereby potentially releasing unintendedNO_(x) emissions. Thus, it is often desirable to periodically perform adiagnostic check on the NO_(x) sensor regardless of a high engine-outNO_(x) spike.

Implementations described herein address methods and systems to detectwhen the NO_(x) sensor is in the stuck-in-range failure mode. An enginecontroller or other diagnostic controller may initiate a diagnosticprocess when the NO_(x) sensor initially reaches an operationaltemperature threshold but prior to reducing the O₂ in the exhaust gassample by using the oxygen pumping electrodes. That is, the diagnosticprocess may utilize the O₂ cross-sensitivity of the portion of theNO_(x) sensor that detects the amount of NO_(x) present in the exhaustgas to detect whether the NO_(x) sensor is in the stuck-in-range failuremode when the NO_(x) sensor initially reaches its operationaltemperature. For instance, prior to reducing the O₂ in the exhaust gassample by using the oxygen pumping electrodes, O₂ may be present in thesecond, inner chamber of a NO_(x) sensor (e.g., approximately 1000 ppm)such that the current generated by pumping the oxygen ions throughoxygen porous material should generate a large spike in current whenactivated based on the presence of the O₂ (if 1000 ppm of O₂ is present,the current should register a spike corresponding to an approximately2000 ppm oxygen ion spike based on the 1000 ppm of O₂). If such a largespike in current is present, then the NO_(x) sensor is likely not in thestuck-in-range failure mode. However, if the large spike in current isnot present (e.g., the current remains constant or registers minimalchanges), then the NO_(x) sensor may be in the stuck-in-range failuremode. The current may be converted into a numerical value, such asthrough an A/D converter, to generate a numerical value for a parameterindicative of the O₂ and/or NO_(x) detected by the NO_(x) sensor.

The engine controller or other diagnostic controller may also initiate adiagnostic process during operation. That is, the diagnostic process maystop or reduce the amount of O₂ that is removed from the exhaust gassample by the oxygen pumping electrodes to increase the amount of O₂present in the second, inner chamber of the NO_(x) sensor such that thecurrent generated by pumping the oxygen ions through oxygen porousmaterial should generate a large spike in current based on the increasedpresence of the O₂. If such a large spike in current is present, thenthe NO_(x) sensor is likely not in the stuck-in-range failure mode.However, if the large spike in current is not present (e.g., the currentremains constant or registers minimal changes), then the NO_(x) sensormay be in the stuck-in-range failure mode.

In some implementations, the change in the parameter indicative of theO₂ and/or NO_(x) detected by the NO_(x) sensor (e.g., ΔDetectedNO_(x))may be stored after each diagnostic process. A counter may be utilizedand incremented each time a diagnostic process is run. After apredetermined threshold value for the counter is reached (e.g., 50times, 100 times, 1000 times, etc.) an average of the changes in theparameters indicative of the O₂ and/or NO_(x) detected by the NO_(x)sensor during each diagnostic process may be determined and compared toa stored threshold value. If the average change in the parameterindicative of the O₂ and/or NO_(x) detected by the NO_(x) sensor isbelow the stored threshold value, a parameter may be set to a valueindicating that the NO_(x) sensor is in the stuck-in-range failure mode,a warning lamp may be lit, such as a malfunction indicator lamp (MIL),and/or other indicators that the NO_(x) sensor is in the stuck-in-rangefailure mode may be utilized.

II. Overview of Aftertreatment System

FIG. 1 depicts an aftertreatment system 100 having an example reductantdelivery system 110 for an exhaust system 190. The aftertreatment system100 includes a diesel particulate filter (DPF) 102, the reductantdelivery system 110, a decomposition chamber or reactor 104, a SCRcatalyst 106, and a sensor probe 150.

The DPF 102 is configured to remove particulate matter, such as soot,from exhaust gas flowing in the exhaust system 190. The DPF 102 includesan inlet, where the exhaust gas is received, and an outlet, where theexhaust gas exits after having particulate matter substantially filteredfrom the exhaust gas and/or converting the particulate matter intocarbon dioxide.

The decomposition chamber 104 is configured to convert a reductant, suchas urea, aqueous ammonia, or diesel exhaust fluid (DEF), into ammonia.The decomposition chamber 104 includes a reductant delivery system 110having a dosing module 112 configured to dose the reductant into thedecomposition chamber 104. In some implementations, the urea, aqueousammonia, DEF is injected upstream of the SCR catalyst 106. The reductantdroplets then undergo the processes of evaporation, thermolysis, andhydrolysis to form gaseous ammonia within the exhaust system 190. Thedecomposition chamber 104 includes an inlet in fluid communication withthe DPF 102 to receive the exhaust gas containing NO_(x) emissions andan outlet for the exhaust gas, NO_(x) emissions, ammonia, and/orremaining reductant to flow to the SCR catalyst 106.

The decomposition chamber 104 includes the dosing module 112 mounted tothe decomposition chamber 104 such that the dosing module 112 may dose areductant, such as urea, aqueous ammonia, or DEF, into the exhaust gasesflowing in the exhaust system 190. The dosing module 112 may include aninsulator 114 interposed between a portion of the dosing module 112 andthe portion of the decomposition chamber 104 to which the dosing module112 is mounted. The dosing module 112 is fluidly coupled to one or morereductant sources 116. In some implementations, a pump (not shown) maybe used to pressurize the reductant source 116 for delivery to thedosing module 112.

The dosing module 112 is also electrically or communicatively coupled toa controller 120. The controller 120 is configured to control the dosingmodule 112 to dose reductant into the decomposition chamber 104. Thecontroller 120 may include a microprocessor, an application-specificintegrated circuit (ASIC), a field-programmable gate array (FPGA), etc.,or combinations thereof. The controller 120 may include memory which mayinclude, but is not limited to, electronic, optical, magnetic, or anyother storage or transmission device capable of providing a processor,ASIC, FPGA, etc. with program instructions. The memory may include amemory chip, Electrically Erasable Programmable Read-Only Memory(EEPROM), erasable programmable read only memory (EPROM), flash memory,or any other suitable memory from which the controller 120 can readinstructions. The instructions may include code from any suitableprogramming language.

In certain implementations, the controller 120 is structured to performcertain operations, such as those described herein in relation to FIGS.3-5. In certain implementations, the controller 120 forms a portion of aprocessing subsystem including one or more computing devices havingmemory, processing, and communication hardware. The controller 120 maybe a single device or a distributed device, and the functions of thecontroller 120 may be performed by hardware and/or as computerinstructions on a non-transient computer readable storage medium.

In certain implementations, the controller 120 includes one or moremodules structured to functionally execute the operations of thecontroller 120. In certain implementations, the controller 120 mayinclude a NO_(x) sensor diagnostic module for performing the operationsdescribed in reference to FIGS. 3-5. The description herein includingmodules emphasizes the structural independence of the aspects of thecontroller 120 and illustrates one grouping of operations andresponsibilities of the controller 120. Other groupings that executesimilar overall operations are understood within the scope of thepresent application. Modules may be implemented in hardware and/or ascomputer instructions on a non-transient computer readable storagemedium, and modules may be distributed across various hardware orcomputer based components. More specific descriptions of certainembodiments of controller operations are included in the sectionreferencing FIGS. 3-5.

Example and non-limiting module implementation elements include sensorsproviding any value determined herein, sensors providing any value thatis a precursor to a value determined herein, datalink and/or networkhardware including communication chips, oscillating crystals,communication links, cables, twisted pair wiring, coaxial wiring,shielded wiring, transmitters, receivers, and/or transceivers, logiccircuits, hard-wired logic circuits, reconfigurable logic circuits in aparticular non-transient state configured according to the modulespecification, any actuator including at least an electrical, hydraulic,or pneumatic actuator, a solenoid, an op-amp, analog control elements(springs, filters, integrators, adders, dividers, gain elements), and/ordigital control elements.

The SCR catalyst 106 is configured to assist in the reduction of NO_(x)emissions by accelerating a NO_(x) reduction process between the ammoniaand the NO_(x) of the exhaust gas into diatomic nitrogen, water, and/orcarbon dioxide. The SCR catalyst 106 includes an inlet in fluidcommunication with the decomposition chamber 104 from which exhaust gasand reductant is received and an outlet in fluid communication with anend 192 of the exhaust system 190.

The exhaust system 190 may further include a diesel oxidation catalyst(DOC) in fluid communication with the exhaust system 190 (e.g.,downstream of the SCR catalyst 106 or upstream of the DPF 102) tooxidize hydrocarbons and carbon monoxide in the exhaust gas.

The sensor probe 150 may be coupled to the exhaust system 190 to detecta condition of the exhaust gas flowing through the exhaust system 190.In some implementations, the sensor probe 150 may have a portiondisposed within the exhaust system 190, such as a tip of the sensorprobe 150 may extend into a portion of the exhaust system 190. In otherimplementations, the sensor probe 150 may receive exhaust gas throughanother conduit, such as a sample pipe extending from the exhaust system190. While the sensor probe 150 is depicted as positioned downstream ofthe SCR catalyst 106, it should be understood that the sensor probe 150may be positioned at any other position of the exhaust system 190,including upstream of the DPF 102, within the DPF 102, between the DPF102 and the decomposition chamber 104, within the decomposition chamber104, between the decomposition chamber 104 and the SCR catalyst 106,within the SCR catalyst 106, or downstream of the SCR catalyst 106. Inaddition, two or more sensor probes 150 may be utilized for detecting acondition of the exhaust gas, such as two, three, four, five, or sizesensor probes 150 with each sensor probe 150 located at one of theforegoing positions of the exhaust system 190. In some implementations afirst sensor probe 150 may be upstream of the SCR catalyst 106 and asecond sensor probe 150 may be downstream of the SCR catalyst 106. Inother implementations, the first sensor probe 150 may be upstream of thedecomposition chamber 104 and the second sensor probe 150 may bedownstream of the SCR catalyst 106. In still other implementations, thefirst sensor probe 150 may be upstream of the DPF 102, and the sensorprobe 150 may be downstream of the SCR catalyst 106. Still furtherconfigurations for the sensor probes 150 may be implemented.

III. Implementations of NO_(x) Sensors

FIG. 2 depicts a block diagram of an example NO_(x) sensor 200. TheNO_(x) sensor 200 includes a base 202 that includes an oxygen porousmaterial, such as ZrO₂, that permits O₂ to be pumped through thematerial via electrodes on opposing sides of the oxygen porous materialof the base 202. An exhaust gas sample from an exhaust system, such asexhaust system 190, is received via an inlet opening 204 in the base202. In some implementations, the NO_(x) sensor may have the inletopening 204 positioned within a portion of the exhaust system and/or anexhaust gas sampling component may direct a portion of the exhaust gasto the inlet opening 204. The base 202 of the NO_(x) sensor 200 candefine a first, outer chamber 210 and a second, inner chamber 220. Thefirst, outer chamber 210 may include an oxygen pumping electrode 212such that O₂ present in an exhaust gas to be sampled by the NO_(x)sensor 200 may be removed while allowing the NO_(x) present in theexhaust gas sample to proceed to the second, inner chamber 220. An outerelectrode 230 is positioned such that a voltage differential is formedbetween the oxygen pumping electrode 212 and the outer electrode 230through the oxygen porous material of the base 202 when a voltage (V₀)is applied to the oxygen pumping electrode 212 and the outer electrode230. The pumping current (Ip₀) for the circuit including the oxygenpumping electrode 212 and the outer electrode 230 is proportional to alinear amount of O₂ pumped out of the first, outer chamber 210. That is,the amount of O₂ pumped out of the first, outer chamber 210 can beregulated based on the voltage (V₀) applied to alter the pumping current(Ip₀).

O₂ is removed via the oxygen pumping electrode 212 because of thecross-sensitivity of a NO_(x) decomposition electrode 224 of the second,inner chamber 220 to O₂. That is, during normal operation, the voltage(V₀) can be regulated such that the O₂ present in the exhaust gas sampleis pumped out when the exhaust gas sample is in the first, outer chamber210 to reduce the amount of O₂ in the exhaust gas sample to a minimalamount, such as approximately 0.001 parts per million (ppm), when theexhaust gas sample enters the second, inner chamber 220 of the NO_(x)sensor.

In some implementations, the second, inner chamber 220 may also includean oxygen pumping electrode 222 such that additional O₂ present in anexhaust gas to be sampled by the NO_(x) sensor 200 may be removed. Theouter electrode 230 and/or a separate outer electrode may be positionedsuch that a voltage differential is formed between the oxygen pumpingelectrode 222 and the outer electrode 230 through the oxygen porousmaterial of the base 202 when a voltage (V₁) is applied to the oxygenpumping electrode 222 and the outer electrode 230. The pumping current(Ip₁) for the circuit including the oxygen pumping electrode 222 and theouter electrode 230 is proportional to a linear amount of O₂ pumped outof the second, inner chamber 220. That is, the amount of O₂ pumped outof the second, inner chamber 210 can be regulated based on the voltage(V₁) applied to alter the pumping current (Ip₁). In someimplementations, the voltage (V₁) can be regulated such that the O₂present in the exhaust gas sample is pumped out to further reduce theamount of O₂ in the exhaust gas sample.

The second, inner chamber 220 also includes a NO_(x) decompositionelectrode 224 for the NO_(x) sensor 200. The NO_(x) decompositionelectrode 224 may be ceramic type metal oxide, such as yttria-stabilizedzirconia (YSZ), or any other suitable NO_(x) decomposition electrode224. The NO_(x) decomposition electrode 224 decomposes the NO_(x)present in the exhaust gas sample into nitrogen and oxygen such thations can flow through the oxygen porous material of the body 202 to areference electrode 240 opposite the NO_(x) decomposition electrode 224when a voltage (V₂) is applied to the NO_(x) decomposition electrode 224and the reference electrode 240. The pumping current (Ip₂) for thecircuit including the NO_(x) decomposition electrode 224 and thereference electrode 240 is proportional to the oxygen ions pumped out ofthe second, inner chamber 220 via the NO_(x) decomposition electrode 224and the reference electrode 240. Thus, if only minimal amounts of O₂remain in the exhaust gas sample when decomposed by the NO_(x)decomposition electrode 224, then the resulting pumping current (Ip₂) issubstantially proportional to the NO_(x) present in the exhaust gassample. The pumping current (Ip₂) may be measured as representative ofthe NO_(x) present in the exhaust gas sample. The measured pumpingcurrent (Ip₂) may be converted from an analog measured current to adiscretized digital value using an A/D converter to generate a numericalvalue for a parameter indicative of the NO_(x) present in the exhaustgas sample.

As noted above, the NO_(x) decomposition electrode 224 iscross-sensitive to O₂. Thus, any O₂ present in the exhaust gas sample isalso decomposed into oxygen ions and will affect the pumping current(Ip₂). During operation of the NO_(x) sensor 200, the oxygen pumpingelectrodes 212, 222 are used to minimize the amount of O₂ present in theexhaust gas sample such that the resulting pumping current (Ip₂) issubstantially indicative of the NO_(x) present in the exhaust gassample. However, such cross-sensitivity of the NO_(x) decompositionelectrode 224 to O₂ may be used to determine whether the NO_(x) sensor200 is still operating properly or if the NO_(x) sensor 200 may be inthe stuck-in-range failure mode. That is, by using an increased O₂concentration present in the second, inner chamber 220, either when theNO_(x) sensor 220 first reaches an operating temperature or temporarilyduring operation, the NO_(x) sensor 200 may be diagnosed for such astuck-in-range failure mode.

IV. Implementations of Processes for Detecting Stuck-in-range Failure ofNO_(x) Sensors

FIG. 3 is a block diagram representing an implementation of an exemplaryprocess 300 for detecting a failure of a NO_(x) sensor, such as NO_(x)sensor 200 of FIG. 2, when the NO_(x) sensor reaches an operatingtemperature. The process 300 may be performed by the controller 120 ofFIG. 1, a module of the controller 120 of FIG. 1 (such as a NO_(x)sensor diagnostic module), or another controller or module.

Before the NO_(x) sensor warms up to its operating temperature, there isno removal of O₂ from the first, outer chamber. Thus, there may be asubstantial quantity of O₂ present in the second, inner chamber of theNO_(x) sensor, such as more than 1000 ppm of O₂ in the second, innerchamber. When the NO_(x) sensor reaches its operating temperature, areading of the NO_(x) and/or O₂ present in the second, inner chamber canbe performed (e.g., based on the pumping current (Ip₂) that isproportional to the oxygen ions decomposed by NO_(x) decompositionelectrode 224 when a voltage is applied). Because there has been littleor no removal of O₂ from within the NO_(x) sensor, the reading of theNO_(x) and/or O₂ present in the second, inner chamber should be high,such as approximately 2000 ppm. If the reading is low, such as under 100ppm, then this may indicate that the NO_(x) sensor is in thestuck-in-range failure mode. If the reading is higher than such a lowreading, then this may indicate that the NO_(x) sensor is not in thestuck-in-range failure mode. In some instances, a threshold valueindicative of an amount of O₂ and/or NO_(x) of approximately 100 ppm,500 ppm, 1000 ppm, etc. may be compared to the reading of the NO_(x)and/or O₂ present in the second, inner chamber. Accordingly,implementations of the process 300 for detecting a failure of a NO_(x)sensor when the NO_(x) sensor reaches an operating temperature can beused to detect whether the NO_(x) sensor is in the stuck-in-rangefailure mode.

The process 300 includes activating a NO_(x) sensor diagnosticresponsive to a NO_(x) sensor initially reaching an operationaltemperature (block 310). In some implementations, such as an engine withan aftertreatment system utilizing a system outlet NO_(x) sensor, whenthe engine is initially started, the exhaust gas temperature and theNO_(x) sensor temperature must be raised above one or more temperaturethresholds before the NO_(x) sensor will operate and the aftertreatmentsystem reduces NO_(x). For instance, after the exhaust systemtemperature is increased above a dew point, the NO_(x) sensor may beginto be heated, such as through a heating element of the NO_(x) sensorand/or a portion of diverted heated exhaust gas. The NO_(x) sensor maybe heated to a predetermined operational temperature before the NO_(x)sensor is capable of pumping O₂ from the first, outer chamber and/or thesecond, inner chamber to measure NO_(x). Thus, after the NO_(x) sensorinitially reaches an operational temperature, but before O₂ pumpingbegins to reduce the amount of O₂ present in the chambers of the NO_(x)sensor, a NO_(x) sensor diagnostic may be activated (block 310). As O₂remains in the second, inner chamber of the NO_(x) sensor, if the NO_(x)decomposition electrode and reference electrode of the NO_(x) sensorhave a voltage applied, the NO_(x) decomposition electrode decomposesany O₂ and NO_(x) in the second, inner chamber.

The resulting pumping current (Ip₂) can be measured and converted into adiscretized numerical value (e.g., via an A/D converter) proportional tothe oxygen ions decomposed by the NO_(x) decomposition electrode. Thus,any O₂ present in the exhaust gas sample is also decomposed into oxygenions and will affect the measured pumping current (Ip₂). The discretizednumerical value of the measured current (Ip₂) can be associated with aparameter, such as a parameter for the sampled oxygen/NO_(x) (SONOX). Insome implementations, the parameter and the associated discretizednumerical value for the measured current (Ip₂) may be stored in a datastorage device, such as a memory. The memory may include a memory chip,Electrically Erasable Programmable Read-Only Memory (EEPROM), erasableprogrammable read only memory (EPROM), flash memory, or any othersuitable memory from which data may be written and read from. In someimplementations, the data storage may be part of a controller, such ascontroller 120 of FIG. 1.

The process 300 includes interpreting one or more values of a parameterindicative of a current induced by decomposition of O₂ and/or NO_(x) bya NO_(x) decomposition electrode (block 320). As noted above, the NO_(x)decomposition electrode disassociates any O₂ and NO_(x) in the second,inner chamber, and the resulting pumping current (Ip₂) can be measuredand converted into a discretized numerical value (e.g., via an A/Dconverter) proportional to the oxygen ions decomposed by the NO_(x)decomposition electrode. The discretized numerical value of the measuredcurrent (Ip₂) can be associated with a parameter, such as a parameterfor the sampled oxygen/NO_(x) (SONOX). In some implementations, theinterpretation of the one or more values of the parameter indicative ofthe current induced by decomposition of O₂ and/or NO_(x) by a NO_(x)decomposition electrode may be directly interpreted without being storedin a storage device or, in other implementations, the values of theparameter may be retrieved from the storage device to be interpreted.Thus the interpretation of the one or more values of the parameterencompass interpreting a value for the parameter that results fromreading a value for the current from the NO_(x) sensor, either directlyor indirectly. In some implementations, several values for the parametermay be interpreted, such as a series of values over a predetermineddiagnostic measurement window, such as 1 second, 2 seconds, 3 seconds, 4seconds, 5 seconds, 10 seconds, etc.

The process 300 also includes calculating a variation of the one or morevalues of the parameter (block 330). The calculation of the variationmay include calculating a difference between a first interpreted valueof the parameter and a second interpreted value of the parameter (e.g.,a minimum measured value and a maximum measured value during thediagnostic measurement window), between an interpreted value of theparameter and a predetermined value (e.g., a stored diagnostic basevalue), and/or between an interpreted value of the parameter and apreviously interpreted value of the parameter (e.g., from a priordiagnostic test). The calculated variation may be a change in theparameter proportional to the O₂ and/or NO_(x) detected by the NO_(x)sensor (e.g., ΔDetectedNO_(x)).

The process 300 further includes determining if the calculated variationexceeds a threshold (block 340). The threshold may be a predeterminedvalue stored in a data storage device, such as a memory, to be accessedwhen determining if the calculated variation exceeds the threshold. Thepredetermined value may be an empirically determined value such that,when the calculated variation does not exceed the predetermined value,the NO_(x) sensor is likely in the stuck-in-range failure mode. Thepredetermined value may be a value indicative of an amount of O₂ and/orNO_(x) of approximately 100 ppm, 500 ppm, 1000 ppm, etc. In someimplementations, the predetermined value may be a value indicative of anamount of O₂ and/or NO_(x) of less than 100 ppm, less than 500 ppm, lessthan 1000 ppm, etc. The determination of if the calculated variationexceeds the threshold may include subtracting the calculated variationfrom the threshold and determining whether the resulting value is above,below, or equal to zero.

The process 300 also includes indicating a failure of the NO_(x) sensorresponsive to determining the calculated variation does not exceed thethreshold (block 350). In some implementations, indicating a failure ofthe NO_(x) sensor may include setting a value for a parameter to a valueindicating that the NO_(x) sensor is in the stuck-in-range failure mode(e.g., setting NOxSensorFail=1 if the NO_(x) sensor is in thestuck-in-range failure mode), causing a warning lamp to be lit (e.g., amalfunction indicator lamp (MIL)), and/or other setting any otherindicators that the NO_(x) sensor is in the stuck-in-range failure mode.In some implementations, other processes may be triggered and/or stoppedresponsive to determining the calculated variation does not exceed thethreshold and/or the indicated failure of the NO_(x) sensor. In someimplementations, indicating a failure of the NO_(x) sensor may beresponsive to a predetermined number of calculated variations notexceeding the threshold, such as indicating a failure of the NO_(x)sensor if 10 calculated variations do not exceed the threshold from asample of 20 calculated variations, thereby reducing the likelihood of afalse-positive indication of a failed NO_(x) sensor.

FIG. 4 depicts a block diagram of an implementation of another exemplaryprocess 400 for detecting a failure of a NO_(x) sensor, such as NO_(x)sensor 200 of FIG. 2, during operation. The process 400 may be performedby the controller 120 of FIG. 1, a module of the controller 120 of FIG.1 (such as a NO_(x) sensor diagnostic module), or another controller ormodule.

The process 400 may include activating a NO_(x) sensor diagnostic duringoperation (block 410). In some implementations, the activating of theNO_(x) sensor diagnostic during operation may occur responsive to atimer reaching a threshold, such as activating the NO_(x) sensordiagnostic at predetermined time intervals. In other implementations,the activating of the NO_(x) sensor diagnostic may be activatedresponsive to another event triggering the activation of the NO_(x)sensor diagnostic.

The process 400 includes increasing an amount of O₂ to which a NO_(x)decomposition electrode is exposed (block 420). The increasing of theamount of O₂ may be effected by reducing or stopping the amount of O₂pumped out of the first, outer chamber and/or second, inner chamber ofthe NO_(x) sensor. The reduction of the amount of O₂ being pumped outmay be done via reducing or disconnecting the voltage applied to thecorresponding oxygen pumping electrodes, such as oxygen pumpingelectrode 212 or oxygen pumping electrode 222 of FIG. 2. Thus, theincrease in O₂ remaining in the second, inner chamber of the NO_(x)sensor when reducing or stopping the amount of O₂ pumped out of via theoxygen pumping electrodes may result in the NO_(x) decompositionelectrode and reference electrode of the NO_(x) sensor decomposing boththe O₂ and NO_(x) in the second, inner chamber. The resulting pumpingcurrent (Ip₂) can be measured and converted into a discretized numericalvalue (e.g., via an A/D converter) proportional to the oxygen ionsdisassociated by the NO_(x) decomposition electrode. The increased O₂present in the exhaust gas sample is also decomposed into oxygen ionsand will affect the measured pumping current (Ip₂). The discretizednumerical value of the measured current (Ip₂) can be associated with aparameter, such as a parameter for the sampled oxygen/NO_(x) (SONOX). Insome implementations, the parameter and the associated discretizednumerical value for the measured current (Ip₂) may be stored in a datastorage device, such as a memory. The memory may include a memory chip,Electrically Erasable Programmable Read-Only Memory (EEPROM), erasableprogrammable read only memory (EPROM), flash memory, or any othersuitable memory from which data may be written and read from. In someimplementations, the data storage may be part of a controller, such ascontroller 120 of FIG. 1.

The process 400 includes interpreting one or more values of a parameterindicative of a current induced by decomposition of O₂ and/or NO_(x) bya NO_(x) decomposition electrode (block 430). As noted above, the NO_(x)decomposition electrode decomposes any O₂ and NO_(x) in the second,inner chamber, and the resulting pumping current (Ip₂) can be measuredand converted into a discretized numerical value (e.g., via an A/Dconverter) proportional to the oxygen ions decomposed by the NO_(x)decomposition electrode. The discretized numerical value of the measuredcurrent (Ip₂) can be associated with a parameter, such as a parameterfor the sampled oxygen/NO_(x) (SONOX). In some implementations, theinterpretation of the one or more values of the parameter indicative ofthe current induced by decomposition of O₂ and/or NO_(x) by a NO_(x)decomposition electrode may be directly interpreted without being storedin a storage device or, in other implementations, the values of theparameter may be retrieved from the storage device to be interpreted.Thus the interpretation of the one or more values of the parameterencompass interpreting a value for the parameter that results fromreading a value for the current from the NO_(x) sensor, either directlyor indirectly. In some implementations, several values for the parametermay be interpreted, such as a series of values over a predetermineddiagnostic measurement window, such as 1 second, 2 seconds, 3 seconds, 4seconds, 5 seconds, 10 seconds, etc.

The process 400 also includes calculating a variation of the one or morevalues of the parameter (block 440). The calculation of the variationmay include calculating a difference between a first interpreted valueof the parameter and a second interpreted value of the parameter (e.g.,a minimum measured value and a maximum measured value during thediagnostic measurement window), between an interpreted value of theparameter and a predetermined value (e.g., a stored diagnostic basevalue), and/or between an interpreted value of the parameter and apreviously interpreted value of the parameter (e.g., from a priordiagnostic test). The calculated variation may be a change in theparameter proportional to the O₂ and/or NO_(x) detected by the NO_(x)sensor (e.g., ΔDetectedNO_(x)).

The process 400 further includes determining if the calculated variationexceeds a threshold (block 450). The threshold may be a predeterminedvalue stored in a data storage device, such as a memory, to be accessedwhen determining if the calculated variation exceeds the threshold. Thepredetermined value may be an empirically determined value such that,when the calculated variation does not exceed the predetermined value,the NO_(x) sensor is likely in the stuck-in-range failure mode. Thepredetermined value may be a value indicative of an amount of O₂ and/orNO_(x) of approximately 100 ppm, 500 ppm, 1000 ppm, etc. In someimplementations, the predetermined value may be a value indicative of anamount of O₂ and/or NO_(x) of less than 100 ppm, less than 500 ppm, lessthan 1000 ppm, etc. The determination of whether the calculatedvariation exceeds the threshold may include subtracting the calculatedvariation from the threshold and determining whether the resulting valueis above, below, or equal to zero.

The process 400 also includes indicating a failure of the NO_(x) sensorresponsive to determining the calculated variation does not exceed thethreshold (block 460). In some implementations, indicating a failure ofthe NO_(x) sensor may include setting a value for a parameter to a valueindicating that the NO_(x) sensor is in the stuck-in-range failure mode(e.g., setting NOxSensorFail=1 if the NO_(x) sensor is in thestuck-in-range failure mode), causing a warning lamp to be lit (e.g., amalfunction indicator lamp (MIL)), and/or other setting any otherindicators that the NO_(x) sensor is in the stuck-in-range failure mode.In some implementations, other processes may be triggered and/or stoppedresponsive to determining the calculated variation does not exceed thethreshold and/or the indicated failure of the NO_(x) sensor. In someimplementations, indicating a failure of the NO_(x) sensor may beresponsive to a predetermined number of calculated variations notexceeding the threshold, such as indicating a failure of the NO_(x)sensor if 10 calculated variations do not exceed the threshold from asample of 20 calculated variations, thereby reducing the likelihood of afalse-positive indication of a failed NO_(x) sensor.

FIG. 5 is a process diagram of an implementation of an exemplary process500 for detecting a failure of a NO_(x) sensor, such as NO_(x) sensor200 of FIG. 2, using a counter for determining an average change in aparameter indicative of the O₂ and/or NO_(x) detected by the NO_(x)sensor over several determined values. The process 500 may be performedby the controller 120 of FIG. 1, a module of the controller 120 of FIG.1 (such as a NO_(x) sensor diagnostic module), or another controller ormodule.

The process 500 begins (block 510) and includes activating a NO_(x)sensor diagnostic (block 520). The activation of the NO_(x) sensordiagnostic may be responsive to a NO_(x) sensor initially reaching anoperational temperature (e.g., as described in reference to FIG. 3) orduring operation (e.g., as described in reference to FIG. 4).

The process 500 includes calculating a variation of a parameterindicative of a current induced by decomposition of O₂ and/or NO_(x) bya NO_(x) decomposition electrode (block 530). As noted above, the NO_(x)decomposition electrode decomposes any O₂ and NO_(x) in the second,inner chamber, and the resulting induced pumping current (Ip₂) can bemeasured and converted into a discretized numerical value (e.g., via anA/D converter) proportional to the oxygen ions decomposed by the NO_(x)decomposition electrode. The discretized numerical value of the measuredcurrent (Ip₂) can be associated with a parameter, such as a parameterfor the sampled oxygen/NO_(x) (SONOX). In some implementations, severalvalues for the parameter may be utilized, such as a series of valuesover a predetermined diagnostic measurement window, such as 1 second, 2seconds, 3 seconds, 4 seconds, 5 seconds, 10 seconds, etc.

The calculation of the variation may include calculating a differencebetween a first value of the parameter and a second value of theparameter (e.g., a minimum measured value and a maximum measured valueduring the diagnostic measurement window), between a value of theparameter and a predetermined value (e.g., a stored diagnostic basevalue), and/or between a value of the parameter and a previous value ofthe parameter (e.g., from a prior diagnostic test). The calculatedvariation may be a change in the parameter proportional to the O₂ and/orNO_(x) detected by the NO_(x) sensor (e.g., ΔDetectedNO_(x)). Thecalculated variation of the parameter may be stored in a data structureof a data storage device, such as a memory. The memory may include amemory chip, Electrically Erasable Programmable Read-Only Memory(EEPROM), erasable programmable read only memory (EPROM), flash memory,or any other suitable memory from which data may be written and readfrom. In some implementations, the data storage may be part of acontroller, such as controller 120 of FIG. 1.

The process 500 further includes incrementing a diagnostic counter(block 540) and determining if the diagnostic counter is greater than(or, in some implementations, equal to) an event threshold value (block550). The event threshold value may be a predetermined or preselectednumber of samples of calculated variations to be used to determinewhether the NO_(x) sensor has failed. The even threshold value may beselected or determined to reduce the likelihood of false-positivesindicating the failure of the NO_(x) sensor. If the diagnostic counteris not greater than the event threshold value (block 550), then theprocess 500 returns to activating a NO_(x) sensor diagnostic (block520), which may be responsive to a NO_(x) sensor initially reaching anoperational temperature (e.g., as described in reference to FIG. 3) orduring operation (e.g., as described in reference to FIG. 4). If thediagnostic counter is greater than the event threshold value (block550), then the process 500 continues.

The process 500 includes calculating an average of the calculatedvariations (block 560). The calculation of the average of the calculatedvariations may include accessing stored calculated variations of theparameter from a storage device and dividing by the number of calculatedvariations. The process 500 further includes determining if the averageof the calculated variations is less than (or, in some implementations,and/or equal to) a threshold value (block 570). The threshold may be apredetermined value stored in a data storage device, such as a memory,to be accessed when determining if the average of the calculatedvariations is less than (or, in some implementations, and/or equal to)the threshold value. The predetermined value may be an empiricallydetermined value such that, when the calculated variation is less thanthe predetermined value, the NO_(x) sensor is likely in thestuck-in-range failure mode. The predetermined value may be a valueindicative of an amount of O₂ and/or NO_(x) of approximately 100 ppm,500 ppm, 1000 ppm, etc. In some implementations, the predetermined valuemay be a value indicative of an amount of O₂ and/or NO_(x) of less than100 ppm, less than 500 ppm, less than 1000 ppm, etc. If the average ofthe calculated variations is not less than (or, in some implementations,and/or equal to) the threshold value (block 570), then the process 500returns to activating a NO_(x) sensor diagnostic (block 520), which maybe responsive to a NO_(x) sensor initially reaching an operationaltemperature (e.g., as described in reference to FIG. 3) or duringoperation (e.g., as described in reference to FIG. 4). If the average ofthe calculated variations is less than (or, in some implementations,and/or equal to) the threshold value (block 570), then the process 500continues.

The process 500 includes indicating a failure of a NO_(x) sensor (block580) if the average of the calculated variations is less than (or, insome implementations, and/or equal to) the threshold value (block 570).In some implementations, indicating a failure of the NO_(x) sensor mayinclude setting a value for a parameter to a value indicating that theNO_(x) sensor is in the stuck-in-range failure mode (e.g., settingNOxSensorFail=1 if the NO_(x) sensor is in the stuck-in-range failuremode), causing a warning lamp to be lit (e.g., a malfunction indicatorlamp (MIL)), and/or other setting any other indicators that the NO_(x)sensor is in the stuck-in-range failure mode. In some implementations,other processes may be triggered and/or stopped responsive todetermining the calculated variation does not exceed the thresholdand/or the indicated failure of the NO_(x) sensor.

FIG. 6 is a graphical plot 600 of several values over a period of timefor a parameter indicative of a NO_(x) concentration level from a NO_(x)sensor 610, a parameter indicative of whether a dew point has beenreached 620, a parameter indicative of whether a NO_(x) output value isstable 630, and a parameter indicative of an O₂ concentration level inthe exhaust 640. The values for the parameter indicative of a NO_(x)concentration level from a NO_(x) sensor 610 show a spike 612 when theNO_(x) sensor reaches an operating temperature and the O₂ concentrationin the second, inner chamber is measured using the process 300 of FIG.3. The presence of the spike 612 is indicative of the NO_(x) sensor notbeing in a stuck-in-range failure mode as the NO_(x) sensor measured thelarge amount of O₂ present in the second, inner chamber of the NO_(x)sensor. If the spike 612 was not present and/or indicated a value orvalues are below the threshold value, then the NO_(x) sensor may beindicated as in the stuck-in-range failure mode.

FIG. 7 is another graphical plot 700 of several values for a parameterindicative of a NO_(x) concentration level from a NO_(x) sensor 710, aparameter indicative of whether a dew point has been reached 720, aparameter indicative of whether a NO_(x) output value is stable 730, aparameter indicative of an O₂ concentration level in the exhaust 740 andparameters indicative of a diagnostic trigger count and a diagnosticcompletion count 750.

The values for the parameter indicative of a NO_(x) concentration levelfrom a NO_(x) sensor 710 showing several spikes 712 during operation,such as might be measured implementing process 400 of FIG. 4. Thepresence of the spikes 712 is indicative of the NO_(x) sensor not beingin a stuck-in-range failure mode as the NO_(x) sensor measured theincreased amount of O₂ present in the second, inner chamber of theNO_(x) sensor during the diagnostic process. If the spikes 712 were notpresent and/or indicated a value or values are below the thresholdvalue, then the NO_(x) sensor may be indicated as in the stuck-in-rangefailure mode.

FIG. 8 is a block diagram representing an implementation of the process300 for detecting a failure of a NO_(x) sensor, such as NO_(x) sensor200 of FIG. 2, according to one embodiment. The process 300 shown inFIG. 8 may be performed by the controller 120 of FIG. 1, a module of thecontroller 120 of FIG. 1 (such as a NO_(x) sensor diagnostic module), oranother controller or module. FIG. 8 illustrates that the process 300 isimplemented such that the calculation of the variation may be insteadreplaced by determining if the first interpreted value of the parameterexceeds a threshold value (e.g., the predetermine value, the previouslyinterpreted value of the parameter, etc.) (block 800). FIG. 8 alsoillustrates that the process 300 is implemented such that indicating afailure of the NO_(x) sensor responsive to determining the calculatedvariation does not exceed the threshold may be instead replaced byindicating a failure of the NO_(x) sensor responsive to determining theone or more values does not exceed the threshold (block 802).

The term “controller” encompasses all kinds of apparatus, devices, andmachines for processing data, including by way of example a programmableprocessor, a computer, a system on a chip, or multiple ones, a portionof a programmed processor, or combinations of the foregoing. Theapparatus can include special purpose logic circuitry, e.g., an FPGA oran ASIC. The apparatus can also include, in addition to hardware, codethat creates an execution environment for the computer program inquestion, e.g., code that constitutes processor firmware, a protocolstack, a database management system, an operating system, across-platform runtime environment, a virtual machine, or a combinationof one or more of them. The apparatus and execution environment canrealize various different computing model infrastructures, such asdistributed computing and grid computing infrastructures.

A computer program (also known as a program, script, or code) can bewritten in any form of programming language, including compiled orinterpreted languages, declarative or procedural languages, and it canbe deployed in any form, including as a standalone program or as amodule, component, subroutine, object, or other unit suitable for use ina computing environment. A computer program may, but need not,correspond to a file in a file system. A program can be stored in aportion of a file that holds other programs or data (e.g., one or morescripts stored in a markup language document), in a single filededicated to the program in question, or in multiple coordinated files(e.g., files that store one or more modules, sub programs, or portionsof code).

While this specification contains many specific implementation details,these should not be construed as limitations on the scope of what may beclaimed, but rather as descriptions of features specific to particularimplementations. Certain features described in this specification in thecontext of separate implementations can also be implemented incombination in a single implementation. Conversely, various featuresdescribed in the context of a single implementation can also beimplemented in multiple implementations separately or in any suitablesubcombination. Moreover, although features may be described above asacting in certain combinations and even initially claimed as such, oneor more features from a claimed combination can in some cases be excisedfrom the combination, and the claimed combination may be directed to asubcombination or variation of a subcombination.

As utilized herein, the term “substantially” and any similar terms areintended to have a broad meaning in harmony with the common and acceptedusage by those of ordinary skill in the art to which the subject matterof this disclosure pertains. It should be understood by those of skillin the art who review this disclosure that these terms are intended toallow a description of certain features described and claimed withoutrestricting the scope of these features to the precise numerical rangesprovided unless otherwise noted. Accordingly, these terms should beinterpreted as indicating that insubstantial or inconsequentialmodifications or alterations of the subject matter described and claimedare considered to be within the scope of the invention as recited in theappended claims. Additionally, it is noted that limitations in theclaims should not be interpreted as constituting “means plus function”limitations under the United States patent laws in the event that theterm “means” is not used therein.

The terms “coupled,” “connected,” and the like as used herein mean thejoining of two components directly or indirectly to one another. Suchjoining may be stationary (e.g., permanent) or moveable (e.g., removableor releasable). Such joining may be achieved with the two components orthe two components and any additional intermediate components beingintegrally formed as a single unitary body with one another or with thetwo components or the two components and any additional intermediatecomponents being attached to one another.

The terms “fluidly coupled,” “in fluid communication,” and the like asused herein mean the two components or objects have a pathway formedbetween the two components or objects in which a fluid, such as water,air, gaseous reductant, gaseous ammonia, etc., may flow, either with orwithout intervening components or objects. Examples of fluid couplingsor configurations for enabling fluid communication may include piping,channels, or any other suitable components for enabling the flow of afluid from one component or object to another.

It is important to note that the construction and arrangement of thesystem shown in the various exemplary implementations is illustrativeonly and not restrictive in character. All changes and modificationsthat come within the spirit and/or scope of the describedimplementations are desired to be protected. It should be understoodthat some features may not be necessary and implementations lacking thevarious features may be contemplated as within the scope of theapplication, the scope being defined by the claims that follow. Inreading the claims, it is intended that when words such as “a,” “an,”“at least one,” or “at least one portion” are used there is no intentionto limit the claim to only one item unless specifically stated to thecontrary in the claim. When the language “at least a portion” and/or “aportion” is used the item can include a portion and/or the entire itemunless specifically stated to the contrary.

1-8. (canceled)
 9. A system comprising: a NO_(x) sensor; and acontroller configured to: increase an amount of O₂ in a chamber of theNO_(x) sensor; interpret one or more values of a parameter indicative anamount of O₂ and/or NO_(x) measured by the NO_(x) sensor; determine ifthe one or more values of the parameter exceed a threshold value; andindicate a failure of the NO_(x) sensor responsive to the one or morevalues of the parameter do not exceed the threshold value.
 10. Thesystem of claim 9, wherein the controller is further configured to:calculate a variation of the one or more values of the parameterindicative of the amount of O₂ and/or NO_(x) measured by the NO_(x)sensor; wherein determining if the one or more values of the parameterexceed a threshold value comprises determining if the calculatedvariation exceeds the threshold value; and wherein indicating thefailure of the NO_(x) sensor is responsive to the calculated variationnot exceeding the threshold value.
 11. The system of claim 9, whereinincreasing the amount of O₂ in the chamber of the NO_(x) sensorcomprises deactivating an oxygen pump of the NO_(x) sensor.
 12. Thesystem of claim 9, wherein increasing the amount of O₂ in the chamber ofthe NO_(x) sensor comprises reducing an amount of O₂ removed via anoxygen pump of the NO_(x) sensor.
 13. The system of claim 9, whereinindicating the failure of the NO_(x) sensor comprises setting a valuefor a parameter to a value indicating that the NO_(x) sensor is in thestuck-in-range failure mode.
 14. The system of claim 9, whereinindicating the failure of the NO_(x) sensor comprises lighting amalfunction indicator lamp.
 15. The system of claim 9, wherein the oneor more values of the parameter indicative the amount of O₂ and/orNO_(x) measured by the NO_(x) sensor are based on a measured pumpingcurrent.
 16. The system of claim 9, wherein the threshold value is avalue indicative of an amount of O₂ and/or NO_(x) of less than 100 ppm.17. The system of claim 9, wherein the threshold value is a valueindicative of an amount of O₂ and/or NO_(x) of less than 500 ppm. 18-21.(canceled)